Hi Cal,
I spent two summers there kiting and working as an instructor on Oahu. I've also kited and windsurfed Maui on several occasions.
if you are a learner, go to Kailua Bay. It is about a 2o minute drive from the airport. Lots of holiday rentals if you google it. Winds to expect in August in Kailua are around 15-18 knots from sun up until around 11am, then the winds die down for about two to three hours so you can have lunch then they pick up again from around 2 until sunset with the hour of power (hour before sunset) giving the strongest winds.
Most Oahu kiters use 15/16 and 11/12 combos for the windier days. Take a light wind board or hire one when you are there.
North shore of Oahu, Mokulaiea is around 20-25 knots most days but is not suitable for a beginner. Kites to use are 11/12 or 9/10.
Maui is usually very windy and very gusty. Take an 11/12 and a 7/8
Hey Undage, April is before the windy trade wind season, so take a surfboard and catch the last of the winter swells. Not much wind around at that time of year. Their season starts in May, where they get the odd few dasy until the trades start blowing. You could get anything in that month so a full quiver from 15 to 7 will be required if you wanna get out at all costs. I'd rent if I were you, it'll be easier than carting bulk kites especially if you dont need to use them.
Good winds,